Synthesis and Determination of the Kinetic Parameters for Non-Isothermal Decomposition of Complexes Ln(thd)3phen

Abstract:

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In this work the kinetics of the thermal decomposition of two ß-diketone lanthanide
complexes of the general formula Ln(thd)3phen (where Ln = Nd+3 or Tm+3, thd = 2,2,6,6-
tetramethyl-3,5-heptanodione and phen = 1,10-phenantroline) has been studied. The powders
were characterized by several techniques. Thermal decomposition of the complexes was
studied by non-isothermal thermogravimetry techniques. The kinetic model that best describes
the process of the thermal decomposition of the complexes it was determined through the
method proposed by Coats-Redfern. The average values the activation energy obtained were
136 and 114 kJ.mol-1 for the complexes Nd(thd)3phen and Tm(thd)3phen, respectively. The
kinetic models that best described the thermal decomposition reaction the both complexes
were R2. The model R2 indicating that the mechanism is controlled by phase-boundary
reaction (cylindrical symmetry) and is defined by the function g(α) = 2[1-(1-a)1/2], indicating
a mean reaction order. The values of activation energy suggests the following decreasing
order of stability: Nd(thd)3phen > Tm(thd)3phen.

Abstract: Recently, highly luminescent lanthanide complexes with mixed ligands such as and
β-diketone and two herobiaryl ligands have been synthesized and suggested as promising
light-conversion molecular devices as described by several authors. The synthesis,
luminescence, quantum yields, spectroscopic characteristics, structure, among others
properties of these complexes, including the possibility of production thin film films from
these materials have been discussed, but little is known about their thermal decomposition
kinetics. In this work we report the determination of kinetic parameters of thermal
decomposition of the complexes Gd(thd)3phen and Er(thd)3phen (thd=2,2,6,6-tetramethyl-3,5-
heptanodione; phen=1,10-phenantroline) using the method proposed by Ozawa (1965). The
kinetic parameters obtained for activation energy were: 90 and 87 kJ.mol-1, the values of
frequency factor were: 2.3x107 and 2.0x107 s-1 for Gd(thd)3phen and Er(thd)3phen,
respectively. On the kinetic energy of the complexes, we notice the following order in thermal
stability: Gd(thd)3phen < Er(thd)3phen.

Abstract: A new schiffbase ligand, methyl-2-pyridyl ketone benzoyl hydrazone (L), and its complexes with rare earth nitrates have been synthesized. These new complexes with the general formula of Ln(L)2(NO3)3·nH2O(where Ln = La, n = 5.5; Ce, Pr, n = 5; Nd, Eu, n = 4 ) were characterized by mass spectra, elemental analysis, IR spectra, thermal analysis, UV spectra, molar conductivity and luminescent spectra. All the complexes are stable in air. The results show that the lanthanide ion in each complex are coordinated by oxygen and nitrogen atoms of the ligand, the oxygen atoms of the nitrate and coordinated water molecules. The amide-oxygen atoms of L coordinate to the Ln ions in its keto-form. Tentative structures for the complexes have been proposed.